Conventionally, lower olefins such as ethylene and propylene are produced via steam cracking of hydrocarbon feedstocks including ethane, propane, naphtha, gasoil and hydrowax. An alternative route to lower olefins is the so-called oxygenate-to-olefin process. In such oxygenate-to-olefin process, an oxygenate such as methanol or dimethylether (DME) is provided to a reaction zone containing a suitable oxygenate conversion catalyst, typically a molecular sieve-comprising catalyst, and converted into ethylene and propylene. In addition to the desired lower olefins, a substantial part of the oxygenate is converted into C4+ olefins and paraffins.
In WO2009/065848 is disclosed an oxygenate-to-olefin process wherein the yield of lower olefins is increased by recycling a fraction comprising C4+ olefins to the reaction zone. At least part of the C4+ olefins in the recycle are converted into the desired lower olefins. A disadvantage of the process of WO2009/065848 is, however, that at least part of the recycle stream needs to be purged in order to avoid undesired accumulation of paraffins in the recycle stream. With the purge, also valuable C4+ olefins will be removed from the process without being converted into lower olefins.
In U.S. Pat. No. 7,923,591 is disclosed a process for manufacturing lower olefins from an oxygenate-containing reaction mixture, wherein a product stream comprising C4 and C5 hydrocarbons from the oxygenate conversion step is subjected to extractive distillation to separate saturated butanes from it. The remaining butenes and C5 hydrocarbons are, after solvent stripping, recycled to the oxygenate conversion step.